Author
Topic: APS-C lens mm are correct (Read 26542 times)

you might want to check and see that your settings were correct, because its more than possible, that you may have overlooked what you had set it to, and in amazement rushed to the forums with a new discovery.

That.. or you saying something you know not to be true and get excited by the responses, maybe?

PackLight

No sorry didn't work. The FF body had image showed slightly over 2.5x the total area of the target I was using.

Rather than just telling you that you are wrong.If need to figure out why there is a discrepancy in sizes this is it.A Full Frame sensor is 24x36mm A lens no matter what length focuses approximately the same size on either the FF or Crop SensorThe 7D's sensor is 14.9x22.3 mm. The focused image being the same size the 7D only covers a smaller portion of the image. The FF sensor is 1.6x taller and 1.6 times wider so it only senses a smaller area of the focused light circle.

EF-S lenses and EF lenses for the most part an 18mm lens is an 18mm lens regardless. (less manufacturing discrepancies).

The relationship has nothing to do with the length of lenses. It is only a comparison of sensor size and FOV comparisons between a Full Frame and Crop sensor with equal length lenses.

But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.

Because the lens IS 18-135 in focal length. 24mm on the 18-135 is the same as 24mm on the 24-105 when mounted on the same camera...because focal length doesn't rely on the sensor at all. But, focal length is just one part of the equation; the other being the sensor. A larger sensor leads to a wider field of view (and thus what seems to be a "longer" focal length on APS-C cameras).

APS-H has a 1.3x crop factorNikon APS-C has a 1.5x cropCanon APS-C has 1.6x crop4/3rd has a 2x crop...the list goes on. Imagine how incredibly confusing it would be trying to mount an old Nikon 28mm AI lens onto a Canon APS-C body if that 28mm was just a marketing name for what the lens appeared to be on Nikon crop camera (this is the equivalen of Canon printing 29-216 on the lens). I'd have to divide by 1.5 and multiply by 1.6 to get what it would be, which is insanely confusing. The same would be true of people usign old Canon FD lenses on 4/3rds cameras (divide by 1.6, multiply by 2...it gets silly) But, since focal length is a fixed property regardless of sensor, they print that, because its standardized.

rj79in

If I'm wrong I'll be the first to admit it, I'm not a proud person. I will check it again right now and see if I had done it incorrectly.

But why doesn't Canon print on the lens itself 29-216mm? The 18-135mm printing is misleading then.

The reason why Canon doesn't do that is that the lens really is an 18-135 lens, i.e. when you are shooting the lens at 18mm, the lens is actually at 18mm. It is only that the "field of view" is "cropped". This field of view on a FF sensor would be achieved at an equivalent focal length of 29mm. That's why the APS-C are called cropped sensors.

Test configuration:Canon 7D with EF-S 18-135mm at 35mm (I looked at file data and confirmed it was at exactly 35mm)Canon film Rebel with EF 35-80mm (just turned the lens to 35mm and looked through the viewfinder. Didn't need to take a picture)

Results: I was wrong. The Canon film Rebel was wider at 35mm with the EF lens than the 7D was at 35mm with the EF-S lens. How embarrassing. At least I learned something.

I made up these photos for m,y photo club to show point of view of different focal lengths. All taken from my balcony without moving the tripod. I shot 15, 24, 50, 100, 200, 400, and 800mm with a 5D2, and a 7D, but only show 15, 50, and 800 below. In the Photo below, FF is on the left, 7D 1.6X crop is on the right.

Like I stated, focal length is an intrinsic property of the lens. They don't print 29-216mm on the 18-135mm lens because that would be a lie. The fact that the FF equivalent figures are used in marketing is partly because bigger sounds better (as pointed out above) and partly historical, when everyone was new to digital and coming from the original FF 'sensor' aka 35mm film.

Here's one more for you to wrap your head around, Tristan944: the 'crop factor' applies to aperture, too, in terms of depth of field for the same framing. Because of the narrower AoV with APS-C, to take the 'same shot' (e.g. fill the frame with a 6' tall subject), at any given focal length you must be further from that subject with an APS-C camera compared to FF. That increased distance means deeper DoF, by a factor of 1.6x (which is a linear measure, when converted to a base-2 log it's 1.3-stops). So...the real FF equivalent of your 18-135mm f/3.5-5.6 lens would be a hypothetical 29-216mm f/5.6-9 lens (in terms of DoF; sensor size doesn't affect exposure, since that's determined by light per unit area of sensor, independent of sensor size).

Not exactly. They are better if you are talking about using all of them on the same APS-C body. But if you compare the EF-S lens on APS-C to the L lens on FF, the latter will deliver better overall IQ (although worse in some measures, especially distortion).

Neuro, just out of interest, I realise that this is only one example so not applicable in general, but from what I have seen and read, my understanding is that the EF-S 10-22 does a better job at the wide end than the 17-40L does, with regards to resolution (specifically wide open corner resolution) and distortion.

Not exactly. They are better if you are talking about using all of them on the same APS-C body. But if you compare the EF-S lens on APS-C to the L lens on FF, the latter will deliver better overall IQ (although worse in some measures, especially distortion).

Neuro, just out of interest, I realise that this is only one example so not applicable in general, but from what I have seen and read, my understanding is that the EF-S 10-22 does a better job at the wide end than the 17-40L does, with regards to resolution (specifically wide open corner resolution) and distortion.

That's actually why I emphasized 'overall'. A current FF sensor will deliver more spatial resolution (measured in LW/PH) than a current APS-C sensor. The extreme corners of the 17-40L at 17mm are an exception, but even at the borders (well away from the center, but not at the extreme corner), the 17-40 at 17mm f/4 delivers higher resolution than the 10-22mm does anywhere in the frame at any focal length and aperture.

at the borders (well away from the center, but not at the extreme corner), the 17-40 at 17mm f/4 delivers higher resolution than the 10-22mm does anywhere in the frame at any focal length and aperture.

I am probably being simplistic here, but the slrgear tests of those 2 lenses completely refute that claim. But they use 'blur index' which may differ from your strict term 'resolution'. My summary statement would be the 17-40 is a little less blurred in the border and corners than the 10-22's borders and corners at similar equivalent focal lengths and apertures.

They also show the 10-22 having the lower distortion in the 10-17mm range than the 17-40 has in the 17-30 range.

Not my intent, sorry...the 10-22mm is a great lens, IMO. Do note that I called out distortion specifically, that's notoriously difficult to control in a FF ultrawide lens, and much easier to control with the smaller elements used in an EF-S lens.

The EF-S 17-55mm, 15-85mm, and 10-22mm lenses all deliver optical performance that is on par with many L-series lenses, and in fact, those lenses all outperform 'sort of equivalent' L-series lenses when comparing both on the same APS-C camera (e.g. the 17-55mm is better than the 16-35L II and 24-105L when comparing all of them on a 7D - and I know this from both test charts and personal experience). But when you put a different camera into the equation, and compare an EF-S lens on APS-C to an L-series lens on a recent FF/APS-H body, the larger sensor confers some IQ advantages. So, for example, the 16-35L II on a 5DII will deliver better overall performance (although barrel distortion is definitely worse) than the equivalent framing of the 10-22 on a 7D (again, from both charts and my own real-world experience having used both combos). The IQ of the 10-22mm in the 7D is already very good, it's just that the 16-35 + FF is slightly better.

You can see an aspect of that in the real world (sort of) with people who've popped off the rubber piece on the 10-22's lens mount and used it on a 1DIV - the 10-22 delivers images on the APS-H that are better than those from an APS-C body.